A shut-off device for a window raising motor is described in German disclosure document DE-AS No. 12 10 690. That device eliminates limit switches for the drive motor. Another purpose of that device is to switch off the window raising motor when the user carelessly places his hand on the edge of the window pane. When a force is exerted on the window pane, the motor develops an increased torque and draws an increased current. The motor is shut off by sensing this increase in torque. A safety relay is provided for switching off the drive motor in case of overload. This safety relay establishes a connection between the actuating relays provided for each direction of rotation of the motor, which connection causes both relays to pull in to stop the drive motor, regardless of the contact position of a manual switch for operating the motor.
German disclosure document DE-AS No. 21 63 746 describes an electromechanical device to prevent pinching. One of the purposes of that design is to eliminate the disadvantage of contact strips arranged in pairs, which form a closed circuit when they touch each other. Such contact strips may be deformed if exposed to certain forces, and then form a permanent short circuit. As set forth in that disclosure, a rope is provided in an elastic rubber gasket; and the rope is used to operate a switch. However, this device is a complicated mechanism that is subject to failure; and it cannot be used for automobile windows.
Alternatively, a device has been proposed which limits the closing force of the window pane to a maximum value, while using a substantially greater force to open the window. See German disclosure document DE-AS No. 15 30 992. In that design the speed-torque characteristic of a motor is reduced appropriately by means of a third brush when the motor turns in the direction which closes the window. Further reductions of the torque exerted in closing the window are, however, not permissible due to the requirement that the window raising motor must securely close the window even if component wear causing increased friction occurs with the progress of time. For stricter requirements a separate motor would be required.
Mechanical devices for controlling the torque of a window raising motor are disclosed, for example, in German disclosure documents DE-OS Nos. 18 01 339, 19 31 169 and 20 28 195. According to DE-OS No. 19 31 169 a slip clutch can be made ineffective by means of a bridging jumper switched on by an additional manual switch. According to DE-OS No. 20 28 195 the bridging jumper is disconnected when the motor turns in the direction which causes the window to open.
Electric eyes are proposed for monitoring the doors of vehicles according to German disclosure document DE-OS No. 15 80 284. The requirements for the automatic operation of doors, however, are quite different from those for the operation of automobile windows.